I've released the second version of Frankfurter4J, a Java implementation of the Frankfurter.dev API to retrieve reference exchange rates.

var latestRates = new LatestRates.Builder()
        .amount(100.0)
        .base("USD")
        .symbols("EUR", "GBP")
        .build();
var exchangeRates = latestRates.exchangeRates();
var euro = exchangeRates.rateFor("EUR");
var britishPound = exchangeRates.rateFor("GBP");

As usual, source and documentation are on GitHub.